Conventionally, an apparatus of this kind is known that includes a sine-wave pressurizing apparatus to apply as a load a sine-wave air vibration pressure to a respiratory system, an air current velocity detector to detect an air current velocity of the respiratory system, an air pressure detector to detect an air pressure of the respiratory system, and a resistance computing unit that calculates breathing resistance from the air current velocity and the air pressure detected by the air current velocity detector and the air pressure detector.
The conventional apparatus: further includes a reference signal converter to convert a signal of the sine-wave air vibration pressure that is applied by the sine-wave pressurizing apparatus into a reference signal and a vector computing device that processes a signal of the air current velocity using the reference signal of the sine-wave air vibration pressure from the reference signal converter and that, thereby, takes out only a component at the same frequency as that of the reference signal; and is adapted to calculate the breathing resistance using the resistance computing unit from the signal of the air current velocity obtained by the vector computing device and the signal of the air pressure detected by the air pressure detector.
As above, this apparatus is adapted to measure the breathing resistance using the resistance computing unit from the signal of the air current velocity obtained by the vector computing device and the signal of the air pressure detected by the air pressure detector and, therefore, noises may be removed even when the amount of ventilation of the breathing is a little and the number of ventilating sessions is large. Therefore the apparatus has an advantage that the apparatus may execute high precision measurement of breathing resistance (see Patent Document 1).
However, the removal of the noises is not sufficient even by the conventional apparatus and realization of a higher-performance respiratory impedance measuring apparatus is demanded.